Due to their design and intended use, a number of vehicles contain a significant amount of empty space (e.g., pick-up trucks, cargo vans, minivans, trailers, 18-wheelers). This empty space creates a weight imbalance that tends to reduce a driver's control on snow and ice. In an attempt to increase traction, many owners of lightweight vehicles place cinder blocks, bricks, sand bags, logs or other heavy items in the cargo space of their vehicles. Not only does this practice reduce the useful area within the vehicle, it also creates a serious risk of injury or death if the items become flying projectiles during an accident or sudden stop. A somewhat safer weighting device is a large rectangular water bladder that may be filled with a garden hose and placed in a trunk of a car or bed of a pick-up truck. However, these bladders contain between 12.5 and 50 gallons of water and weigh between 100 and 400 pounds when full. A puncture of the bladder can therefore release large quantities of water within a trunk or car interior, and removal of an intact bladder may be difficult or impossible when the water within it is frozen. Further, these water bladders have convex top surfaces that are unsuitable for the stable transport of most items.